1. Field of the Invention
The present invention relates to a vestibule which can be attached to a microwave oven which processes products, wherein the vestibule prevents or significantly reduces the amount of microwave radiation escaping into the atmosphere.
2. Discussion of Related Art
Conventional heating or drying typically includes convectional or a combination of convectional and radiative gas or electric resistance heating that is commonly used in the manufacturing of certain materials, such as ceramics. However, the slow heating rate and poor temperature control associated with such conventional heating methods results in high energy consumption and inconsistent product quality. Furthermore, using both of these modes of heating typically results in thermal differences within the body of the processed material because the heat is only applied to the exposed surface of the material from which the product is manufactured. Moreover, the thermal conductivity of the material affects the temperature beneath the exposed surface of the material to the core of the material, which corresponds to the center of the products body.
Heating by microwave radiation has become a popular technique for accelerating the drying process of the products. Compared with convectional heating, microwave heating provides a higher heating rate with good penetration, better temperature control, lower energy consumption, and potentially better quality products. Furthermore, the use of microwave energy provides a uniform application of the energy to the entire product body. Also, microwave heating is significantly faster than the aforementioned conventional methods.
Although microwave heating has proven to be faster and more efficient than conventional heating techniques that use hot air or gases, a major disadvantage of microwave heating in a continuous microwave oven is the control of microwave radiation being emitted into the environment. Such microwave emissions must be controlled in order to comply with emissions regulations established by relevant governmental regulatory agencies (e.g., OSHA, FCC, CEPT). It is preferable that microwave driers operate with nearly zero microwave emissions into the surrounding environment. Typically, the shielding of microwaves in such operations is accomplished by using attenuation tunnels, water traps, and metallic (e.g., aluminum) curtains. Although these devices are effective in most applications, there is an inherent limitation as to the size and shapes of the products which can be heated by the microwave oven associated with the aforementioned shielding device. Further, such shielding devices limit the manipulation of the products passing through the microwave oven, which directly affects the ability of the products to be heated properly and uniformly while being conveyed through the oven.